1. Field of the Invention
The present invention relates to a pattern forming method.
2. Description of the Related Art
Micropatterning is performed in manufacture of various electronic components such as semiconductor integrated circuits including LSIs (Large-Scale Integrated Circuits). It is demanded that resist patterns be formed with so high a precision that the patterns may serve to manufacture electronic components each having a high integration density.
An example of resist for use in micropatterning is chemical amplification-type resist disclosed in, for example, Published Unexamined Japanese Patent Application 63-27829. The resist is a composition which contains an alkali-soluble resin, a dissolution inhibitor and an acid generator. Unless the composition is exposed to light, the dissolution inhibitor inhibits the alkali-soluble resin from being dissolved in an alkaline solution. When the composition is exposed to light, x ray or high-energy electron beam, the acid generator generates an acid. The acid decomposes the dissolution inhibitor as the composition is baked. Namely, this composition is equivalent to a positive type resist any portion of which becomes alkali-soluble when exposed to light, X ray or high-energy electron beam and can thereafter be dissolved in an alkaline developing solution.
The method employed hitherto to form a pattern by using a positive type resist, will be described as follows. First, a substrate is coated with the resist, forming a resist layer. Next, the resist layer is selectively exposed to light. After the exposure, the resist layer is baked and developed with an alkaline developing solution. As a result, the exposed portions of the resist layer are dissolved and removed, thereby forming a desired resist pattern comprising lines and spaces.
The pattern formed by the conventional method using the positive type resist described above may, however, comprise lines each having a cross-section which has a sloped profile, or slopes down to surface of spaces, depending on the material of the substrate. Consequently, the resist pattern has but a limited resolution and cannot be used as a mask in the micropatterning of electronic components. In particular, the resist pattern cannot serve to form extremely narrow grooves or very small contact holes, since the cross-section of each line has a sloped profile.
FIG. 1 is a cross-sectional view of part of a positive type resist pattern 12 formed on a substrate 11 by the conventional method. As shown in FIG. 1, each line of the pattern 12 has a cross-section having a sloped profile. Due to the sloped profile, each line fails to have a prescribed width, and the space between any two adjacent lines have a designed width.
Another example of resist for use in micropatterning is a composition which contains an acid generator, an alkali-soluble resin, and a compound having a substituent group capable of cross-linking the resin in the presence of an acid. When the composition is exposed to light, X rays or high-energy electron beams, the acid generator generates an acid. The acid promotes the cross-linking of the resin as the composition is baked. Hence, this composition is equivalent to a negative type resist any portion of which becomes alkali-insoluble when exposed to light, X ray or high-energy electron beam, and will not be dissolved in an alkaline developing solution.
Hitherto, a pattern of negative type resist is formed by a method similar to the above-described method of forming a pattern of positive type resist. More specifically, a substrate is coated with the negative type resist, forming a resist layer. Next, the resist layer is selectively exposed to light. After the exposure, the resist layer is baked, rendering the exposed portions alkali-insoluble. The resist layer is then developed with an alkaline developing solution. As a result, the unexposed portions of the resist layer are dissolved and removed, whereas the exposed portions remain on the substrate, forming a desired resist pattern.
The formed by the conventional method using the positive type resist pattern may, however, comprise lines each having a cross-section which has an undercut profile, or a narrowed root, depending on the material of the substrate. Consequently, the resist pattern has but a limited resolution and cannot be used as a mask in the micropatterning of electronic components.
FIG. 2 is a cross-sectional view of part of a negative type resist pattern 22 formed on a substrate 21 by the conventional method. As shown in FIG. 2, each line of the pattern 22 has a cross-section having an undercut profile. Due to the undercut profile, each line fails to have a prescribed width, and the space between any two adjacent lines have a designed width.